Experiments proposed in this application will explore the role of macrophage activation in the pathogenesis of the inflammatory bowel diseases (IBD). We will focus on the molecular regulation of IL-12 p40 in macrophages as one of the most biologically significant events in T-helper1 (Th1)-mediated chronic inflammation. We have recently described a novel composite element in the IL-12 p40 promoter that interacts with members of the nuclear factor of activated T cells (NFAT) and interferon regulatory factor (IRF) families of transcription factors. This control element is involved in the synergistic induction of IL-12 p40 promoter activity by bacterial products and interferon-y (IFN-y), and is an important target for inhibition of IL- 12 p40 gene expression through several signal transduction pathways. The overall goal of this proposal is to understand the molecular regulation of IL-12 p40 in experimental models of IBD. Experiments will elucidate the role of two newly appreciated anti-inflammatory signal transduction pathways in macrophages: Heme oxygenase-1 (HO-1) and phosphatidylinositol-3-kinase (PI3K). We hypothesize that these anti-inflammatory pathways converge through regulation of NFAT/IRF interactions at the IL-12 p40 promoter. By inhibiting IL-12 p40, HO-1 and PI3K serve as molecular "brakes" for macrophage activation that may limit the extent and duration of chronic intestinal inflammation. lnterleukin-12 (IL-12) is an inflammatory protein that has been demonstrated to be important in the progression of human Crohn's disease (CD). In this application, we will test therapeutic interventions in mouse models of CD to inhibit IL-12 production by cells of the immune system called macrophages. Studies in this application will give us important information about immune inhibitory pathways that may be defective in human IBD and may lead to new therapeutic interventions in human IBD that target macrophages and IL- 12.